The invention relates to an apparatus for electronic monitoring of the supply current of modules connected to a bus, in particular for monitoring the supply current of bus devices of an automation bus system.
Present day automation systems, that is to say control and data transmission systems, generally have a multiplicity of electronic modules which all have to be supplied with electric energy. For this purpose, the individual modules, for example the bus devices, are connected in parallel to a voltage supply by means of a central power supply unit. A short circuit occurring in a bus device, or an overload which occurs can lead to the consequence that the voltage supply collapses, and thus the other connected modules cannot be further supplied with energy either, and therefore fail. The data traffic in the automation bus system fails, and this finally entails a total failure of the system. Fault location, that is to say locating the fault site, is possible only by virtue of the fact that the individual modules are removed from the system and individually checked, something which is very time-consuming.
In order to prevent the total failure of the system, the modules are frequently connected to a voltage supply by segment or section, an individual segment being protected against short circuits with the aid of a fuse or a miniature circuit breaker. However, in this case the feeding power supply unit must be capable of carrying out the isolation of the relevant segment from the supply in a reliable fashion, if required. In some circumstances, however, tripping the fuse can give rise to difficulties as long as the branch to be protected against short circuits is in overload, but no short circuit is yet present.
The object of the invention is thus to provide an apparatus for electronic monitoring of the supply current of modules connected to a bus, which on the one hand, if required, carries out reliable isolation from the supply voltage, and simultaneously maintains the diagnostics capability for the purpose of fault locating.
This object is already achieved by means of an apparatus having the features of claim 1, and by means of an automation bus system as claimed in claims 15 and 16.
Advantageous developments of the invention are specified in the subclaims.
In order to be able reliably to detect the occurrence of a fault, that is to say an overload or a short circuit inside a module or a connection between the modules, the apparatus according to the invention comprises a device for detecting the flowing supply current. Furthermore, the apparatus has a device for limiting and/or for disconnecting the supply current, which operates in response to the detected supply current, and thereby ensures that the energy supply for other modules of the automation bus, which are connected in parallel with reference to the supply voltage, does not fail, as a result of which at least a limited operation of the system is maintained, and thus fault diagnosis is also possible despite the occurrence of an overload or a short circuit. If the device for detecting the supply current establishes, for example, an impermissibly increased supply current, the supply current for the module connected downstream of and assigned to the apparatus is disconnected in response thereto, or at least limited.
In this case, according to the invention a module can be an arbitrary component or an arbitrary unit, which can be used to design an automation system.
It is possible for the first time with the aid of the invention for bus segments, in the event of a fault or on start-up, to be connected and disconnected in a noninteracting fashion with full maintenance of the diagnostic function, since owing to the isolation of the module which is, for example, defective or has a defective assigned connecting line, only this one module or a single segment of the system with a plurality of modules is isolated from the supply voltage, while the remainder of the system remains in operation.
In order, on the one hand, further to improve the possibility of diagnosis and, on the other hand, to provide communication between the apparatus according to the invention and the controller of the automation system, the apparatus can be connected to the automation bus. Consequently, the apparatus according to the invention can, for example, be caused to disconnect a module, in particular a bus device, by the controller of the system. This signifies a marked improvement in the reliability of such automation bus systems since, for example, unreliable bus devices which no longer react to the customary control commands can be disconnected via the controller. Furthermore, the controller can retrieve the supply current flowing toward the module at any time, and thus make an early detection of overloads which may be developing, and thereupon initiate the necessary measures before the failure of the bus device or the module.
In order to provide a high flexibility of the apparatus according to the invention for the purpose of adaptation to all conceivable requirements, the parameterization of the disconnection, in particular the tripping current and/or the disconnection characteristic, can be performed manually and/or via the bus. Consequently, it is also possible, for example, for the response of the apparatus according to the invention to the detected supply current or to the detected electric load to be modified during operation of the system, and/or the apparatus can be reset centrally to altered conditions, for example to an exchange of a module with a changed supply voltage requirement.
For the purpose of modifiable setting, the apparatus according to the invention can comprise a storage device in which, for example, the limiting value of the supply current, that is to say the value at which, or in the case of the exceeding of which, the device disconnects the supply current, or the supply current is limited, can be stored as tripping current value. Furthermore, the disconnection characteristic or else minimum, maximum and instantaneous values of the supply current can be stored in the storage device, these values being available, for example, in the case of a diagnosis on the apparatus or, for example, a diagnostic program via the automation bus. In addition, time marks assigned to the respective current values can also be stored for the purpose of detecting a temporal variation in the supply current. Furthermore, these values can also be retrieved by the controller at any time.
In order to support the fault locating, and to provide a simple control possibility, it can be provided to render the denoted supply current values readable by means of a display device on the unit or on a display assigned thereto.
In order to prevent inadvertent reconnection of the supply current, the apparatus is automatically locked after the response of the disconnection or of the limitation, and can be cleared only manually or, depending on the embodiment, also via the bus by means of a reset. This is important, in particular, so that a disconnected module is not reconnected inadvertently, something which could entail consequential damage under some circumstances.
The apparatus according to the invention can advantageously also be set up to detect ground faults.
In order to provide flexible adaptation to all conceivable possibilities of use of the apparatus according to the invention, the apparatus can comprise a power supply unit, in order, for example, to adapt a single-phase or three-phase ac voltage to the dc voltage or dc voltages usually required of a bus device. Consequently, together with the additional feature of the bus connection of the apparatus according to the invention the advantageous result is a power supply unit with bus capability in the case of which individual voltages, or all voltages provided, can be connected or disconnected, for example, by means of the controller via the bus, or else manually. If the bus logic circuit and unit logic circuit (for example sensor system or activator system) of a bus device are supplied separately, it is possible, for example, in the case when a short circuit has occurred in the unit logic circuit, for the latter to be specifically disconnected by means of an apparatus according to the invention, as a result of which the bus connection of the bus device continues to remain available, and thus the bus traffic can also be maintained in the relevant segment.
For the purpose of integrating the apparatus according to the invention into an emergency stop system, said apparatus can also have an emergency stop input via which the apparatus can be caused to disconnect the supply current. Furthermore, the apparatus can be set up in such a way that it disconnects the supply voltage in response to at least one safety-related output, for example a signal of a temperature monitor, a humidity sensor, a proximity switch, an overvoltage sensor, an overload sensor or a fire and/or smoke detector. The apparatus according to the invention can therefore be excellently integrated into any desired emergency stop system, it being possible for the supply voltage to be switched both via external inputs, and by means of control signals via the bus.
In order to enhance the possibility of diagnosis, the apparatus can be set up to feed back the disconnection or the limitation of the supply current to the control system. The feedback, in particular via the automation bus, can in this case comprise a data item for identifying the apparatus and/or the at least one module assigned to it. In this way, the system can determine the fault site exactly, or at least determine the section in which, for example, there has been a short circuit when an apparatus for a plurality of modules, for example bus devices, undertakes the monitoring. As a result, the fault locating is substantially simplified, or can in some circumstances be carried out automatically by the system itself.
As already mentioned, the apparatus according to the invention can be used advantageously in an automation bus system which comprises at least a controller, an automation bus and bus devices. For example, in a section of the system which comprises a plurality of bus devices, it is possible to arrange for the purposes of supplying voltage to these bus devices an apparatus according to the invention which is connected upstream of the bus devices, while these bus devices are arranged in parallel with reference to their supply voltage. In this case, a single apparatus according to the invention monitors the supply voltage of a plurality of bus devices. The possibility of diagnosis is limited in this case to the entire section. Owing to the response of the apparatus according to the invention, that is to say the isolation from the supply voltage, the occurrence of an overload in one of the parallel-connected bus devices leads to the disconnection of all the devices.
If, however, an apparatus according to the invention is connected upstream of each bus device in the automation bus system with reference to its supply voltage, in the event of a short circuit or an overload on a specific bus device, this individual bus device can be disconnected specifically and be identified specifically as fault site. In this case, the apparatuses according to the invention can advantageously be connected to the automation bus. If the bus device fails upon disconnection of the supply voltage, the apparatus according to the invention which is assigned to the bus device can, for example, provide the controller via the bus with the required information on the fault site.
If the automation bus is a serial one, for example a bus according to EN 50254, the apparatuses according to the invention can all be connected to a common bus spur, at least in a section of the system. If the bus devices assigned to the respective apparatuses are also connected to a common bus section, which, however, differs from the bus spur of the apparatuses according to the invention, the diagnostics capability is maintained for the apparatuses according to the invention independently of the respective bus devices, since disconnection of the bus section belonging to the bus devices has no effect on the bus spur to which the apparatuses according to the invention are connected on the bus. The system can thus detect completely and unambiguously a failure of bus devices, for example in a local section, and can reconfigure the automation bus system so as to permit further operation of the system.